In the field of this invention an example of a storage device comprising a plurality of scanning probes is a micro-electro-mechanical system (MEMS) based scanning-probe data-storage system. A typical example of such a probe-based storage device that uses thermomechanical writing and thermomechanical or thermal reading by using heater cantilevers is disclosed in Vettiger et al., “The ‘Millipede’—More than one Thousand Tips for Future AFM Data-Storage,” IBM J. Res. Develop., Vol. 44, No. 3, pp. 323-340 (2000); and E. Eleftheriou et al., “Millipede-a MEMS-based scanning-probe data-storage system,” IEEE Trans. Magn., vol. 39, pp. 938-945 (2003). Such a system is also disclosed in U.S. Pat. No. 5,835,477 issued 10 Nov. 1998 to Binnig, G. K. et al.
A main function of a servo system of such storage device is to maintain the position of a read/write probe on the centre of a track during read/write operation. This is known as a track follow mode. Track following controls the fine positioning of the read/write probe in the cross-track direction, and maintains constant the velocity of the scanner in the on-track direction, and is critical for reliable storage and retrieval of user data. It is typically performed in a feedback loop driven by a position error signal (PES), which indicates the deviation of the current position from the track centre line (TCL). Position error signal generation for servo control of storage devices comprising arrays of scanning probes has been addressed in Pozidis, H. et al., “Tracking in the Millipede System,” IBM Research Report RZ 3432, July 2002, as well as EP1385161A2 assigned to the Applicant. It was argued that the use of dedicated storage fields for storing servo information is advantageous in terms of area overhead compared to the alternative of sectored servo schemes, as described for example in Sacks, A. H., “Position signal generation in magnetic disk drives”, Ph.D. Thesis, Carnegie Mellon University, 1995, especially as the number of scanning probes increases. Formatting of servo data stored on servo fields was also addressed, and a method for decoding the servo data into position error signals has been specified.
However, prior to fine tuning a scanning probe to the centreline of a track, the scanning probe first has to be positioned on the right track of a multi-track storage medium. Consequently, in such a storage device it is a challenge to locate the precise track where information is to be written or from which information is to be read.
As during such positioning process no reading or writing of user data may be performed, the duration of these modes has to be kept to a minimum.
A need therefore exists for a method and apparatus allowing fast and accurate settling on a target track in a storage or scanning device comprising a scanning probe.